The axles of most of the railway trucks now in use remain substantially parallel at all times (viewed in plan). A most important consequence of this is that the leading axle does not assume a position radial to a curved track, and the flanges of the wheels strike the curved rails at an angle, causing objectionable noise and excessive wear of both flanges and rails.
Much consideration has been given to the avoidance of this problem, notably the longstanding use of wheels, the treads of which have a conical profile. This expedient has assisted the vehicle truck to negotiate very gradual curves.
However, as economic factors have led the railroads to accept higher wheel loads and operating speeds, the rate of wheel and rail wear becomes a major problem.
A second serious limitation on performance and maintenance is the result of excessive, and even violent, oscillation of the truck at high speed on straight track. In such "nosing", or "hunting", of the truck, the wheelsets bounce back and forth between the rails. Above a critical speed, hunting will be initiated by any track irregularity. Once started, the hunting action will often persist for miles with flange impact, excessive roughness, wear and noise, even if the speed be reduced substantially below the critical value.
In recent efforts to overcome the curving problem, yaw flexibility has been introduced into the design of some trucks, and arrangements have even been proposed which allow wheel axles of a truck to swing and thus to become positioned substantially radially of a curved track. However, such efforts have not met with any real success, primarily because of lack of recognition of the importance of providing the required lateral restraint, as well as yaw flexibility, between the two wheelsets of a truck, to prevent high speed hunting.
For the purposes of this invention, yaw stiffness can be defined as the restraint of angular motion of wheelsets in the steering direction, and more particularly to the restraint of conjoint yawing of a coupled pair of wheelsets in a truck. The "lateral" stiffness is defined as the restraint of the motion of a wheelset in the direction paralleling its general axis of rotation, that is, across the line of general motion of the vehicle. In the apparatus of the invention, such lateral stiffness also acts as restraint on differential yawing of a coupled pair of wheelsets.
The above-mentioned general problems produce many particular difficulties, all of which contribute to excessive cost of operation. For example, there is deterioration of the rail, as well as widening of the gauge in curved track. In straight track, the hunting, or nosing, of the trucks causes high dynamic loading of the track fasteners and of the press fit of the wheels on the axles, with resultant loosening and risk of failure. A corresponding increased cost of maintenance of both trucks and cars also occurs. As to trucks, mention may be made, by way of example, to flange wear and high wear rates of the bolster and of the surfaces of the side framing and its bearing adapters.
As to cars, there occurs excessive center plate wear, as well as structural fatigue and heightened risk of derailment resulting from excessive flange forces. The effects on power requirements and operating costs, which result from wear problems of the kinds mentioned above, will be evident to one skilled in this art.
In brief, the lack of recognition of the part played by yaw and lateral stiffness has led to: (a) flange contact in nearly all curves; (b) high flange forces when flange contact occurs; and (c) excessive difficulty with lateral oscillation at high speed. The wear and cost problems which result from failure to provide proper values of yaw and lateral stiffness, and to control such values, will now be understood.
It is the general objective of my invention to overcome such problems by the use of self-steering wheelsets in combination with novel apparatus which maintains stability at speed, and to this end, I utilize an articulated, self-steering, truck having novelly formed and positioned elastic restraint means which makes it possible to achieve flange-free operation in gradual curves, low flange forces in sharp curves, and good high speed stability.
To achieve these general purposes, and with particular reference to railway trucks, the invention provides an articulated truck so constructed that: (a) each axle has its own, even individual, value of yaw stiffness with respect to the truck framing; (b) such lateral stiffness is provided as to ensure the exchanging of steering moments properly between the axles and also with the vehicle body; and (c) the proper value of yaw stiffness is provided between the truck and the vehicle.
With more particularity, it is an objective flexibly to restrain yawing motion of the axles by the provision of restraining means of predetermined value between the side frames and the steering arms of a truck having a pair of subtrucks coupled through steering arms rigidly supporting the axles. Elastomeric means for this purpose are provided between the axles and the adjacent side frames, preferably in the region of the bearing means. Such means may be provided at one or both axles of the truck. If provided at both axles, it may have either more or less restraint at one axle, as compared with the restraint at the other, depending upon the requirements of the particular truck design.
It is a further object of this invention to provide elastomeric means in the region of the coupling between the arms to restrain lateral axle motions, which limits so-called "differential" yawing of a coupled pair of subtrucks or steering arms.
With the foregoing in mind, the present invention provides a truck assembly for use with a railway vehicle on which the truck is adapted to be mounted, the truck assembly comprising at least two axle-borne wheelsets, a load-bearing truck framing pivotally movable about a vertical axis with respect to the vehicle body, a steering arm for each wheelset having load-bearing portions with axle bearings movable with respect to the framing in the steering sense, mechanism interconnecting the steering arms in the region between the axles independently of the load-bearing framing and enforcing coordinated substantially equal and opposite steering motions of the wheelsets with respect to the truck framing, and mechanism for yieldingly resisting yaw motions of the steering arms including means providing a relatively high rate of increase of resistance per unit of deflection in the initial portion of the yaw motion of the steering arms and means providing a relatively low rate of increase of resistance per unit of deflection in a portion of the motion beyond said initial portion.